1. Field of the Invention
The present invention relates to a head for a thermal assisted magnetic recording device, and a thermal assisted magnetic recording device.
2. Description of the Related Art
In recent years, a thermal assisted magnetic recording system has been proposed as a recording system which realizes a recording density of not less than 1 Tb/in2 (H. Saga, H. Nemoto, H. Sukeda, and M. Takahashi, Jpn. J. Appl. Phys. 38, Part 1, 1839 (1999)). In conventional magnetic recording devices, when recording density becomes 1 Tb/in2 or more, recording information loss due to thermal fluctuations becomes a problem. In order to prevent this, the coercivity of a magnetic recording medium needs to be increased. However, since there are limitations on the intensity of a magnetic field capable of being generated in a recording head, a recorded bit cannot be formed in the medium if the coercivity thereof is increased too much. In order to solve this, in the thermal assisted magnetic recording system, a medium is heated by light at the instant of recording to decrease the coercivity thereof. This enables recording to be performed on a high-coercivity medium, and can realize a recording density of not less than 1 Tb/in2.
In such a thermal assisted magnetic recording device, the spot diameter of light applied needs to be a size approximately equal to that of a recorded bit (several tens of nanometers). This is because information recorded in adjacent tracks is erased if the light spot diameter is larger than the above-described size. To heat such a very small region, an optical near-field is used. An optical near-field is an electromagnetic field (light having a wave number with an imaginary part) which locally exists near a very small object having a size of not more than a light wavelength, and is generated using a very small opening having a diameter of not more than the light wavelength, or a metal scatterer. For example, in Technical Digest of 6th International Conference on Near Field Optics and Related Techniques, the Netherlands, Aug. 27-31, 2000, p 55, an optical near-field generator using a metal scatterer having a triangular shape is proposed as a high-efficiency optical near-field generator. When light is made incident on the metal scatterer, a plasmon resonance is excited in the metal scatterer, and a strong optical near-field is generated at a vertex of the triangle. The use of this optical near-field generator makes it possible to efficiently collect light in a region which is not more than several tens of nanometers in dimension.
Japanese Unexamined Patent Publication No. H05-101329 discloses diffusing Zn or the like into the tip of a main pole. However, this is not used as a scatterer.
In the above-described thermal assisted magnetic recording device, to form a recording mark, it is required that a medium be heated using the optical near-field generator and, at the same time, a strong magnetic field be applied to the same position as the heated point.